Conventionally, a coupling (shaft coupling) which is a machine element has been used for coupling an output shaft of a rotary actuator that makes a rotary reciprocating movement (swing) at a constant angle with a driven body having a shaft.
For example, as shown in FIGS. 5(A) and 5(B), when a driven member 4 is arranged between frames f oppositely placed, the coupling is so structured that one end of the shaft s for holding the driven body 4 is rotatably supported by a bearing b at one of the frames f. The other end of the shaft is coupled by a coupling c to be connected to an output shaft a1 of a rotary actuator a attached to the other one of the frames f. The rotary actuator a is engaged with the frame f by a recess a2 having an anti-vibration rubber, thereby preventing rotation of the entire rotary actuator a as well as suppressing occurrences of vibration.
For the coupling described above, in addition to the cylindrical shape of a general open-ended coupling (hereinafter referred to as “universal coupling”), there are a metal plate spring type, a metal slit type, a resin portion rose type, and a so-called flexible coupling type described in Patent Document 1 which combines a groove and an elastic member. Moreover, there is a magnetic coupling type for coupling a driven body and an output shaft in a non-contact manner such as shown in Patent Document 2. The flexible coupling and the magnetic coupling noted above have the advantage that they can absorb misalignment between the axes of the coupling.